Many English speakers cannot understand basic grammar

Now this really is a big deal for educationalist, linguists and people concerned with communication in various ways (public health, for example). The article is here: Many English speakers cannot understand basic grammar

Now the background to help you clue into why it's a big deal:

"...for decades the theoretical and educational consensus has been solid. Regardless of educational attainment or dialect we are all supposed to be equally good at grammar, in the sense of being able to use grammatical cues to understand the meaning of sentences."

So what has happened to that? Well, they tested people to discover what they thought was the meaning carried by various syntactic constructions.

participants were asked to identify the meaning of a number of simple active and passive sentences, as well as sentences which contained the universal qualifier "every."
As the test progressed, the two groups performed very differently. A high proportion of those who had left school at 16 began to make mistakes. Some speakers were not able to perform any better than chance, scoring no better than if they had been guessing.

One of the interesting results when they were trying to eliminate various other factors:

Participants with low levels of educational attainment were given instruction following the tests, and they were able to learn the constructions very quickly. She speculates that this could be because their attention was not drawn to sentence construction by parents or teachers when they were children.

So it may be that much of this really is down to exposure to certain 'registers' of language. In some ways this is not new: it may be demonstrating that we tend to learn the grammar we are exposed to and have opportunity to practice. In that sense grammar is the same as vocabulary: we don't know the whole potential repertoire, but we can always learn more if we have sufficient motivation and opportunity to practice. And that is important: our ability to learn new linguistic tricks still seems pretty remarkable ...

So the real story here is probably that linguistic diversity within a language is more than we may have realised and may affect syntax more fully than many have given credit for. That said, we should remember some dialectology basics, such as that a dialect is a form of a language with grammatical differences to another (ctr 'accent' which merely differs according to pronunciation). So we are probably dealing with differences which are on a dialectological scale. And, just as pronunciation differences are a statistical continuum along a scale, it may be that the use certain syntax is similarly something that varies along a social scale (whether that scale be determined along social, regional, educational or some other lines).

So it would still be true that this has implications for public notices etc; but we probably should frame it as a dialectological matter (standard English and regional variants, probably). My worry is that some may pick this up as a kind of linguistic disability thing and that probably isn't the real story. Clearly there is a range of ability with language use, but that isn't really the issue here.